Storm chasers to be tracking gusts

Data from Frances, Ivan and other hurricanes confirm a pattern of destructive wind bursts. Researchers hope more observations will inform where, how and what we build.

By GRAHAM BRINK
Published May 29, 2005

Under a cobalt sky, scientist Josh Wurman stood in a Charlotte County mobile home park surveying the fallout from Hurricane Charley.

The storm, he noticed, chewed off roofs and exploded walls of many of the neatly kept homes. Nearby, others went largely unscathed.

A few years ago, Wurman could have chalked up the discrepancy to stronger building materials or superior craftsmanship.

Now, he's not so sure.

It could be the handiwork of a natural phenomenon that can deliver devastating streaks of wind to small areas, sometimes just a few hundred yards across. Wurman has used sophisticated radar equipment to document the effect in several recent hurricanes.

"Before, we just called it gusty," said Wurman, who runs the Center for Severe Weather Research in Boulder, Colo. "Now we know why it's gusty."

The difference could have a lasting impact on how scientists study what's happening near the eye wall of hurricanes, the breeding ground for the most damaging winds. Eventually, the findings could affect how and where we build homes.

It was September 1996, peak hurricane season, as Wurman and his crew raced their research truck from Norman, Okla., to the East Coast.

They hoped the Doppler radar system would provide a high-resolution, multidimensional look inside Hurricane Fran.

But they needed to place the truck, and themselves, in the direct path of the storm.

They settled on an airport in Wilmington, N.C., then waited. They had been up close and personal with many tornadoes, using the Doppler radar to see what was happening inside the twisters. Hurricanes were fresh game.

Wurman wasn't entirely certain the truck, with hundreds of thousands of dollars of equipment on board, would stay upright. And he wasn't sure what would show up on the radar.

"It was a classic fishing expedition," he said.

What the radar captured left Wurman wondering if the equipment malfunctioned. The high resolution screen depicted bright red streaks, representing very fast winds, right next to blue areas of much slower winds.

"That was the eureka moment," Wurman said. "All that red in the wind field."

A further analysis confirmed what Wurman and his crew thought they were seeing. The winds were moving in corkscrew patterns, not vertically like a tornado, but horizontally like giant toy Slinkies stretched almost to the breaking point.

As the Slinkies rotated, they pulled the winds down from about 3,000 feet. In a hurricane, winds at that height are more powerful than the winds at the surface. Each turn of the Slinkies brought down more of the powerful winds, but only into specific areas. Each Slinky measures a few hundred yards across, Wurman says.

As the winds reacted with the surface, they weakened and were taken aloft.

Scientists had observed rolling effects in other weather systems, but nothing like this.

Wurman was hungry to see more.

Great insights

When researchers first deployed the Doppler system, it was like peering through a microscope for the first time. Everything looked cool.

After Fran, Wurman and fellow researchers figured they were on to something. He thought the phenomenon could help explain the sometimes confounding damage patterns hurricanes leave behind.

Eight hurricanes later, including last year's Frances and Ivan, he's certain the phenomenon exists. The specific characteristics remain more elusive. How do they get stronger or weaker? What role does topography play? Can the location of the down gusts be predicted?

Fellow wind researcher Forrest Masters said Wurman's work was a big step forward in answering those questions.

"The work they are doing with the radar is providing great insight into the gust structures, the damaging winds, as they come down into our communities," said Masters, a wind engineer with the International Hurricane Research Center at Florida International University. "Now we need to know what those winds are doing and why they react the way they do."

Masters has helped set up a series of sophisticated wind-gauge towers in the paths of several hurricanes. The hurricane research center also has placed pan-shaped sensors on the roofs of homes in the paths of hurricanes.

Masters hopes the collective research will help determine the strength of the most powerful gusts in any given area.

"That can assist everyone from meteorologists to politicians in making decisions on how to handle a storm," Masters said. "Josh's research helps us move toward that type of reality."

Wurman is particularly interested in how the streaks react with man-made structures.

During Hurricane Frances, he set up two radar trucks a few miles apart. The radar captured the eye as it passed over some tall condominiums on a nearby barrier island. Wurman would like to know whether the buildings slowed the wind gusts or perhaps acted to speed them up. Or maybe groups of buildings have a different effect than single structures.

"Maybe it's good, at least when it comes to these wind gusts in a hurricane, to have tall structures on barrier islands to act as a shield," he said. "Maybe it's bad. We just don't know right now."

Wurman also hopes to discover how the Slinkies react to topographical features such as hills or lowlands. The research could reveal whether certain features act as anchors, allowing the winds to stay in one place and slam a particular area for a lengthy period. Other areas, for some topographical reason, might be less susceptible.

"Whatever we find," he said, "it could have a practical impact on where we build, what we build and how we build."

Chasing storms

Wurman and his crew will be back on the East Coast this hurricane season, chasing the next big storm.

He estimates it will take dozens, if not hundreds, of hurricanes to nail down all the various characteristics of the rotational pattern.

He would like to have spotters in residential areas near the Doppler radar trucks. The spotters would be able to monitor whether roofs flew away or walls caved in at the precise moment the radar trucks recorded one of the gusts.

But the dangerous realities of a hurricane make that problematic, Wurman said.

"There's a reason," Wurman said, "they tell people to evacuate from residential areas."